1. Field of the Invention:
The present invention relates to novel spheroidal silica particulates and to a process for the preparation thereof. This invention more especially relates to novel spheroidal silica particulates having improved macroporosity and to the use thereof as either catalysts or catalyst supports.
2. Description of the Prior Art:
Catalysts or catalyst supports based on silica must generally have a porosity which facilitates a rapid diffusion of surface gases towards the active inner centers thereof, and vice versa. This is the reason why macroporosity is a usual requirement. Furthermore, these catalysts or supports must have a mechanical strength that is, in particular, retained after impregnation thereof with a catalytic active phase, as well as during their use under the conditions of the process in which they are utilized.
Various processes for the production of spheroidal silica particles are known to this art. Thus, German Patent No. 1,266,741 describes the formation, by the sol-gel method, of a silica hydrogel mixed with a solution of an alkaline silicate in the presence of an acid. Drops of the mixture are formed which are allowed to fall and coalesce into a nonmiscible liquid, the spheres obtained being dried, and then calcinated. The principal disadvantage of this process is that it is complicated and delicate to carry out, and yields materials, the cost of production of which is high. Furthermore, the product spheroidal particulates explode on being soaked in water or on being impregnated with solutions containing active catalytic phases.
Furthermore, also proposed to this art have been less difficult processes for the production of spheroidal silica particulates by granulation. Thus, German Patent No. 1,187,588 describes a process in which an aqueous silica sol containing magnesium oxide as binder is mixed with silicated and siliceous charges. The disadvantage of such a process is that it requires the use of a binder, and the resultant porosities are not satisfactory.
Thus, it heretofore has not been possible to economically produce spheroidal silica having adequate macroporosity and satisfactory mechanical strength, particularly upon impregnation with active catalytic phases. Furthermore, the prior art processes have required the use of a binder uncombined with silicon.